Fanconi anemia (FA) is a rare genetic disorder characterized by developmental abnormalities, progressive aplastic anemia, and increased cancer incidence. Although FA pathway is believed to participate in DNA repair, the exact role of this pathway in DNA repair remains to be elucidated. The key function of the FA pathway is to promote FANCD2 monoubiquitination following DNA damage. However, how FANCD2 is recruited to sites of DNA damage is unknown. More importantly, the task of FANCD2 monoubiquitination in DNA repair is still a mystery. We made two discoveries recently, which will likely answer the questions mentioned above. First, when we were studying the newly identified SOSS complexes in DNA repair, we found that these complexes also associated with FANCI and FANCD2. Moreover, we showed that SOSS complexes are required for the efficient chromatin loading, focus formation, and monoubiquitination of FANCI and FANCD2 following DNA damage. These studies suggest that SOSS complexes act together with the FA core complex and participate in the regulation of FANCI/FANCD2 ubiquitination following DNA damage. Second, we discovered that an ubiquitin-binding zinc finger (UBZ) domain-containing nuclease KIAA1018/FAN1 interacted with FANCD2. Our subsequent studies suggested that this protein acts downstream of FANCD2 and participates in DNA repair. We propose that this protein links the FA pathway to DNA damage repair. Moreover, we are also studying another newly identified FA protein SLX4/FANCP, which may act with KIAA1018/FAN1 in DNA repair. Based on these exciting preliminary studies, we propose to: 1) Define the regulation of FANCI/FANCD2 localization via their associations with SOSS complexes; 2) Determine the functional significance of KIAA1018/FAN1 and SLX4/FANCP in DNA repair; 3) Identify the in vivo functions of KIAA1018/FAN1 in the maintenance of genomic stability and tumor suppression. PUBLIC HEALTH RELEVANCE: Fanconi anemia (FA) is a rare genetic disorder characterized by bone marrow failure, developmental abnormalities and high incidence of malignancies. There are at least 15 genes involved in the FA pathway, which are believed to function in DNA damage repair; however, the most critical event in the FA pathway is monoubiquitination of FANCD2. Further study of the regulation and function of FANCD2 monoubiquitination will reveal how cells promote survival and ensure genomic stability following DNA damage, which are critically important for understanding the efficacy of cancer treatments with radiation and chemotherapeutic agents.